Process of desulphurizing petroleum oils



Oct. 7, 1941. T. F. MccoRMlcK PROCESS OF' DESULPHURIAZING PETROLEUM OILS 7 Sheets-Sheet l Original Filed Nov. 16, 1935 I/v V/v TOR THOMAJ E Mc COR/mel( Y A T TOQ/VEY.

T. F. MCCORMICK PROCESS OF DESULPHURIZING PETROLEUM OILS Original Filed Nov. 16, 1955 '7 Sheets-Sheet 2 oct. 7, 1941.

'1'. F. MccoRMlcK Y v 2,258,512 PROCESS OF DESULPHURIZING PETROLEUM OILS V Oct. 7, 1941.

original Filed Nov. 1e, `1955 7 sheets-sheet s `27V VEN 7'0"" THOMAS E Mc CoRM/CK A Troia/var vOct. 7, 1941.

Original Filed Nov. 16, 1935 7 sheets-sheet 4 `f/V VEN TOR. THOMAS EMC CoRM/cf A T ToR/VEY.

oct. 7, 1941. 1 T. F. MCCORMICK 2,258,512

PROCESS 0F DESULPHURIZING PETROLEUM OILS Original Filed NOV. 16, '1935 7 Sheets--Sheec` 5.

I/v VE/v'roa THOMAS EMc CoRM/CK A TTORNEY.

Oct- 7, 19421- T. F. MccoRMlcK v 2,258,512 4 PROCESS OF DESULPHURIZING PETROLEUM `OILS Original Filed Nov. 16, 1935 7 Sheets-Sheet 6 Oct. 7, 1941. T, F McCQRMlCK 2,258,512

PROCESS OF DESULPHURIZING PETROLEUM OILS 'Original Filed Nov. 16, 1955 7 Sheets-Sheet T mlm A TToIQ/vay.

` Patented Oct. 7, 1941 UNITED STATES PATENT VGFFFICIE VIRGCESS `0FfDESUlLPHUItlZI'NG PETROLEUM OILS rlhomas F. McCormick, Oakland, Calif., lassigner Ato Tide Water` Associated -Oil Gompamr, .San Francisco, Calif., a corporation .o` f Delaware Original yapplication Novemberrl, 1935,;Scrial No. Y

50,206. Divided and thiscappli'cation :.Ifuly di, 1938, Serial No..2^17,657

4 Claims.

This invention relates to y'the treatment =of ipetroleum oil, or distillates thereof, and has 'for a particular object the reduction 5of fthe 'sulphur content of cracked distillates with concomitant improvement in color, odor and octane rating.

"The linvention is particularly applicable for the above purposes to a ds'tillate derived from cracking petroleum, or its `fractions -such Vas crackedi'gasoline which is selected forillustration herein, but the invention is not necessarily `limited lto'proce'ssing such gasoline, being'in a broad sense A"directed tothe Vtreatment `of any lpetroleum or `distillate thereof, having characteristics in contorrnitywith this disclosure and responsive to the steps outlined herein.

\ Cracked gasoline is particularly useful for use as Ta fuel in internal combustion engines which, with 'modern `high `compression pressures, require a fuel with relatively hghfoctane number rtoprevent-detonation.

This octane numberwith ordinary cracked gasoline may be obtained by the addition thereto 'of wel1 "known antiknock compounds such as tetraethyl-lead, etc., Abut itis much more preferable and economical to utilize as v-far as possible the antknock Avalues 'in the crude cracked gasoline itself.

This A'is accomplished by the herein described process in so treating a crude cracked gasoline with `sulphuric `acid that the selective solvent action-of lthe acid is exercised in atleast 'two directions, which -may be termed a split-treat, Withgreat Veconomy 'of 4acid Vand large reduction in Sulphur.

Cracked -gasolines vary in lchemical structure, percentage of sulphur, etc., Wththe type of stock used jfor cracking as Well astheJtype-of cracking process employed. In general, `cracked gasolines contain increased percentagesof unsaturated hydrocarbons over the stock from which `theywere derived 'andusually contain ya Asubstantial vquantity of sulphur compounds.

\ "Ihe unsaturated hydrocarbons, `which include the olenes and aromatics; are highly ydesired yin motor fuel as antiknock compounds to reduce, 'or suppress, detonatlon and the problem of retainthe same` during treatment with sulphuric acid :for theyremovalfo'f undesired sulphur is solved.l herein' in a novel and highly useful manner.v y

VIt lhas been determined `that When va total cracked distillate is "carefully 'fractionated by taking a 410% jcut comprising 4 each fraction 'that thelirst few cuts upto aboutQlO arerelatively low'in sulphur whileh being theh'ghest 'in Voctane (Cl. 19E-"31) number. Also, the sameIi-rst :few cuts 'arerclatively lhigh .in :percentage icffunsatura'ted compounds whichzshows conformity with highfoctane number.

The remain-lng 60% fof the. cracked distillate shows incueasing sulphur fcontent sup to :about 70% and .from therefon the end of the 'fractionation a slight :dropin .sulphur `occurs, but no lway to a degree approaching the :low Asulphur content of the .rrstf40%. Y

This maybe better illustrated `by thefollowing table, `which 'is `typical fof California rcracked distillates of :high sulphur :contenu and in which it will be seen `that thei'sulphur content of each 10% fraction fbears .out the above statements, the

sulphur 'being 'expressed fas ya percentage ilby Weight of a particular cracked gasoline traction.

The above-'fractions ara-of course, taken in the usual manner in 4accordance with volatility of the fractions .and .the results -show that amaximum sulphur content is reached when from Vabout 70% to 80% .o'f "the distillatefhas been .taken off.

`If each of .the above .10% 'fractions is "then treated Aindividuallywith lthe same amount of sulphuric acid, for 'instance 498% acid, for the purpose of reducing the sulphur content to a de` sir'ed maximum, it 'may be seen there ,is a large jump inthe sulphur lcontent ofthe heavier fractions of the distillate from 40% on as shown in thev following table: f

This indicates that an amount of sulphuric acid which is sufficient to desulphurize more volatile fractions up to about 40% of the cracked distillate is insufficient to desulphurize the heavier fractions from 40% on. l

The reason for this is believed to be that the sulphur in the lighter and more easily desulphurized fractions is largely in the form of sulphides and mercaptans while in the heavier fractions the sulphur is in a different form, probably 'asl thiophenes.

From this it may be seen that if a cracked total distillate is treated as a-jwholejwith sufficient concentrated sulphuric acid to remove the sulphur from the heavier fractions' thereof, the lighter fractions must then besubjectto a4 sulphuric acid treat far in excess of Yrequirements to remove only sulphur and therefore the desired antiknock compounds of the lighter fractions will respond to the sulphonating and polymerizing action., of the excess concentrated acid andare removed ,in the acid sludge, andre-'run 'distillationwithlarge'losses of the very constituents desired to be retained. y

.This 'defect intreatment -is overcome: inthe present invention byutilizing methods of treating the total cracked distillate wherein the distillate is first separated.byfractionation according'totthe sulphur content of the diierent fractions and each fraction. thus.separated is then treated separately with just suiicient sulphuric acid to removeV the desired amount of sulphur and then the treatedfractions may be blended to form thetotal finished gasoline containing a minimum per-centage of sulphur and a high percentage of `the unsaturates .present in the stock beforeacid ltreatment.; i

The total cracked distillate may be separated into any desired number of fractions to be separately treated with sulphuric acid, but in commercial refinery operations, it is generally suflicient in obtaining the desired results to fractionate the crude cracked distillate, in accordance with boiling ranges, into two or possibly three fractions and then separately treating each fraction in accordance with its sulphur content.

The simplest way is, of course, to divide the total cracked distillate into two parts by fractionation, one part containing from about to 60% o f the lighterfractions relatively low in sulphur 'and relatively'v high in unsaturates, and the other part containing'from about 80% to 40% ofthe heavier'fractions relativelyhigh in sulphur.V Each fraction may then be separately treated'with sulphuric acid ofthe same degree of concentration to assure 'the desired desulphurization but the rate of treatment,` or'pounds of sulphuric acid per barrel', for the lighter fraction will be far less than that required for the heavier fraction. j

`At times it may be desirable to similarly separate the crude total cracked 'distillate into three fractions:

(l) Light fractions relatively low in sulphur and relatively high in unsaturates comprising for instance about from 20% to 40% of the distillate.

(2) Intermediate fractions relatively high in sulphur which, however, is contained in compounds easily absorbed by,V or reactive with, sulphuric acid,iand comprising about from to 50% of the distillate. Y (3) Heavy fractions relatively high in sulphur which, however, 'is contained in compounds of the residual type requiring comparatively large amounts of concentrated sulphuric acid for their removal.

The distillation range of each fraction to be thus separately treated may be easily determined by simple laboratory control to fix the points at which the cuts should be made and at the same time to determine the rate of acid treatment for desired results. Hence, the invention is not limited to any particular fractional division of the total cracked distillate, but is applicable to the treatment of any number of fractions in which the described steps are used. Nor is the invention limited to the treatment of selected fractions for the removal of sulphur and retention of unsaturates, as it is applicable in its broadest sense to the selective application to selected fractions for removal of unsaturates of certain concentrations of sulphuric acid as, for instance, the removal of olenes from the lighter fractions relatively high in unsaturates to recover alcohols from the oleflne containing acid sludge'by hydrolysis.

The preferred application of the invention is.v however, directed to the production of a motor fuel retaining the bulk ofthe unsaturates and one method of treating is shown in the laccompanying drawings, in which:

Fig.,1 is a diagrammatic flow sheet rshowing a split-treat in which a two, or three fraction cut can be used.

Fig. 2 is a diagrammatic flow sheet taken from the co-pending application of Edwards and Stark, Ser. No. 532,000, led April 22, 1931, for use with Fig. l and showing a preferred form of contacting the acid and distillate.

Fig. 3 is a chart illustrating the efficiency of a true countercurrent treatment of a cracked total distillate as shown in Fig. 2 over a batch treatment of the same distillate when treating in both cases with acid of the same concentration to effect the removal of the same percentage of sulphur- Y Fig; 4 is a chart showing the efciency of treating a selected light fraction from a cracked end point distillate by the countercurrent methodof Fig. 2 over a batch treatment of the same fraction when treating in both cases with acid of the same concentration to effect the removal of the same percentage of sulphur.

Fig. 5 is a chart illustrating the eii'iiciency o f treating a selected heavy fraction from a cracked en d point distillate by the countercurrent method of Fig. 2 over a batch treatment of the same fraction when treating in both cases with acid of the same concentration to effect the removal of the same .percentages of sulphur. f n

Fig. 6 is a chart illustrating the efciencyin sulphur removal by batch treatment, comparing the results obtained in sulphur removal by splitting a cracked end point distillate into 50% of a light fraction and 50% of a heavy fraction and treating each fraction separately with acid to the results obtained by treating the cracked end point distillate as a whole; in both cases usingl sulphuric acidYV of i the same concentration.

Fig. 7 is a chart showing the efficiency of treating vthe light and heavy fractions obtainedfrom a cracked end point distillate separately in trueA countercurrent -ow's according f to Fig. 2 over treating the unspiit distillate by the same method; sulphurlcacid of the same concentration bei ing used in both cases and thelight and heavy fraction. each consisting of 50% of the unsplit distiiiateaccording tc voiatiiity. L j,Referring to Figs; 1 and 2,'i'twi11 be seen that 2,258,512- tiffe erakedfaisniiatemayte,passedrtonneeeasiy' through 'line I0 into a still, Jor fractioriator, li-I',

wherein controls 1are 'established in `Well 'known manner tc pass say 50% of theffdi'stillate according to volatility through .suitablecondensers (not shown in line I2 and throug-hfan alkaline. wash I3 suchv as causticsoda, or rsodiumcarbonate, or

other suitable solution, to remove certain impuri-Vv ties such as hydrogen sulphidey and organic `acids,

and the `thus treated lieu-iid fraction is then passedI through Ya, treating -plant I4 (W-hich -is preferably oflthe type shown in Fig. l2) wherein the fraction "is 'subject :to "true :.countercurrent contacting.

I I `passes throughline 20, alkaline Wash 21| ,treati ing plant 2&2., run downtank `23to rerun still IS Where .it blendswit'h thelight treated fraction and is distilled therewith .to end point gasoline., which .is Vthen subjected to the usual sweetening process .24 .bymeans of doctor solution, or other sweetening cprocess, and is .thus nished ready for use... i

.Theheavy .traction is, of course, subject to countercurrent treatment with concentrated sulphuric .acid ,in treating plant 22 .at a much higher rate than that applied to the `lightffraction in treatingplant Ii4 and the acid sludge from treating plant` v22 is collected in tank .25. V

It is found that such acid sludge -obtained from treating the heavy .fraction `in pla-nt 22 with high acid rates. contains .suiiicient reactive sulphurc `acid .to function efliciently for the desulphurization of the light fraction in treating ,pla-nt I4, hence a preferred form of the invention includes the .supply of acid sludgederived from the treatment of the vheavyfraction from sludge tank 25, through line `2li totreating plant vI4 for the treatment of` the light `fraction therein and therate of such supply is, of course, in conformity` Withfrequ-irements for efficient desulphurization of the light fraction to the desired degree. ,l Y

Apparently, the acidsludge produced from-the treatment 'of the heavy fraction at relatively high' acid rates to remove atrelatively Vhigh percentage of sulphunfrom the -heavy fraction, although having accomplished` maximum desulphurization -of the .heavy fraction still retains `sufficient chemical reactivity toy treat .effectively the more unsaturated light fraction Without substantial loss of unsaturates therefrom. In addition,` the use of such sludge accomplished the removal of unstable unsaturates such as the gum forming constituents like di-olenes together with acidsoluble sulphur compounds, all of Which improves the odor and stabilizes .the -color of thelight fraction. ,t

i .1t seems that the `abstracted organic matter in the' acid sludge .acts as .a diluent andits effect. on lthe :more stable. and desired. unsaturated com-v pounds. in the'. light` Ifraction appears to be the same as thatyoflfa/treatment with dilute .sul-p phuric Aaciolso that excessivesulphonation and polymerization 'of desired. unsaturates Vis pre-` vented. M j

Depending, of lcou-rse, on the degree of desolphuriZatiOn Arequired, Ythe light fraction may or maynot be desulphurized to a point suilicient for commercial requirements by the use of the acid sludge from the heavy fraction treating, inasmuch as the sulphur thus removed from the light fraction may only vary from 20% to 50% of the removable sulphur which is often sufcient.

However, the use of other suitable sludges as, for instance, the acid sludge obtained from the -sulphuric acid treatment of straight run gasoline or kerosene, or from other sources, is contemplated .herein vfor the treatment `of the :light .fraction in place of the straight acid treatment, it being understood, -of course, .that if any of the sludges utilized for this ,purpose are wdeiicient Iin acid value for treatment of the light fraction, such .sludge can ble-increased in Jacid concentration 'by the addition of a yrequired amount of fresh acid from tank I5.

Alternatively, if .the acid .sludge Yderived from the iheavy fraction is .not :sufficiently `reactive to reduce the sulphur content of the light fraction to a very low ligure, the 'light .fraction may be further separate-Iy treated with fresh yacid at` `a rate of vsay up to five pounds ,per barrel of :98%

`A similar procedure is used. vvhen the :cracked distillate is split into three fractions, `the :intermediate fraction being passed from still rI'I through alkaline wash 21, treating plant 28, run down tank29 to re--run still I8., where'it isblended :and distilled with the light .and heavy fra-ctionas before described.

If the acid sludge from the intermediate fraction contains .sufficient acid value :it may be `run through line 30 to sludge tank Y25 for use in `desulphurizing the light fraction, otherwise vit may be withdrawn throughline 3iI Treating plants I4, 22 and 28 lare preferably constructed and operated-iin accordance with `the process disclosed in said cao-pending .application Ser. No. 532,000, as illustrated in Fig. 2 hereof, in which .any of the fractions, or the unsplit total distillate, is passed by pump 3I through a Icooler. 32 into the bottom of a'contacttower 33 substantially filled with a suitable `contact material 34, comprising Raschig rings, glass beads, crushed gravel or other well known material, and meets therein in true countericurrent `flow acid sludge from a spray '35 :derived from the succeeding treatment of the distillate and forced through spr-ay by pump 3E.

The :distillate 4thus treated with relatively spent L acid sludge passes through ar-valve .31 into iline tower 46 which is supplied with fresh acid through apump 41 and spray=48.

In this manner, there'is provided 'true countercurrent contacting of the distillate` with the acid, or acid "sludge, in each tower together with true countercurrent flow vof distillate `with acid lsludge l l through thesyst'em so that maximum desulphurization combined with minimum losses of desired hydrocarbons is assured. j

. 'The temperature during the acidtreats in' each contact tower, shouldbe .sufficiently .low to `perm-it selective solvent action of the sulphuric acid on undesired sulphur compounds and gum forming sulphuric acidy to the barrel to recover an acid sludge used-on the light fraction, is illustrative:

constituents while preventing excessive sulphonation and polymerization of unsaturates. Depending on the type of stock treated, concentration of acid used, etc., such treating temperatures may range during reaction from F. to 40 F. or even lower or higher. Simple laboratory tests, Well known to those skilled in the art, will determine the optimumV temperatures taking all things into consideration.

The countercurrent acid treatment of the distillate being iinished in tower 45, the distillate may be passed through line 49 into a settling chamber 50, similarly lled with contact material to separate any entrained acid sludge, and thence through line into a similarly lled contact tower 52, receiving spent caustic sludge through pump 53 and spray 54 from the bottom of a second caustic contact tower 55 supplied with fresh caustic solution, the spent caustic from both towers 52 and 55 being discharged through line 56.

The caustic treatment serves to neutralize any remaining acidity, such as dissolved SO2 and the neutralized distillate is then passed through a line 58 and a wash tower 59, supplied with a water spray through line 69, to a run down line 6I controlled by valve 63, which serves to apply a predetermined pressure of from 50 to 100 pounds per square inch on the system for the purpose of holding SO2 gas in solution.

The discharge of acid sludge is controlled by a valve 62 and the discharge of caustic sludge is controlled by a valve 64 which, together with valve 63, maintain the desired pressure on the system.

As before stated, the acid sludge derived from the treatment of a heavy fraction may be run into tank 25 to be supplied through line 26 for treating the light fraction.

Pumps 36 and 42 serve to withdraw acid sludge as rapidly as possible4 from the bottom of towers 4| and 46 respectively, together with a portion of the distillate from each of said towers for the purpose of establishing iirsta circulatory system for the distillate between two of the towers and secondly to pass the sludge from a succeeding towerV tothe top g of a preceding tower for contacting the cooled distillate therein, the sludge being separated from the accompanying distillate from each pump in the top of each tower due to a reduction in velocity therein where it is sprayed on the contact material evenly and descends countercurrentV to the rising distillate.

I'he increased velocity of thedistillate stream thus circulated between two towers adds largely to the efficiency-of the 'interposed cooling sections 49 and 45.

As an example of treating efficiency in utilizing the acid sludge from the heavy fraction for desulphurizing the light fraction, the following data, derived from operating the above described split-treat when the total cracked distillate is split according to volatility into 55% of a light fraction and 45% of a heavy fraction and treating the heavy fraction with 10 pounds of 98% The sulphur removal will depend in part on the chemical structure of the sulphur compounds present and also on the characteristics and quantity of the sludge obtained from the treatment of the heavy fraction.. With acid rates higher than l0 pounds of 98% acid to the barrel there is naturally a higher desulphurization of the light fraction due to the greater reactivity of the sludge and alsov the desulphurization is greater when using a true countercurrent contact of acid sludge and oil as before described.

The relative efliciencies of batch and true countercurrent contacts are well illustrated in Fig. 3 as well as the relative eiiiciencies of the batch and true counter-current contacts of the light fraction and of the heavy fraction which are shown in Figs. 4 and 5. The relative etciencies between batch treatment of the complete cracked distillate and the same distillate split into a light and a heavy fraction and treated as above described are shown in Fig. 6. The relative efflciencies between true countercurrent treatment of the complete distillate and true counter-current treatment of the light and heavy fractions separately are shown in Fig. 7.

These charts shown in Figs. 3 to 7 inclusive are self-explanatory to those skilled in the art andshow improved desulphurization in every case by use of the herein described process.

In all cases herein where sulphuric acid is used, the tests were made with 98% sulphuric acid and the same isused as illustration only and not as a limitation.

Other strengths of acid can be used depending on operating conditions such as a range of from 66 acid up to 20% fuming sulphuric acid, the concentrations being determined for optimum results by laboratory control. Likewise, the temperature may vary with the concentration of acid and consequent degree of reaction heat between -0 F. up to 80 F.

The rerunning of the light and heavy fractions may be done at one time, or separately, or, when only a light sludge treatment is given the light fraction for stabilization, the rerun distillation thereon may be eliminated.

The total cracked distillate referred to herein is a distillatermade from the pyrolytic cracking of various stocks and is usually a distillate cut to an end point by lS. T. M. distillation similar to normal motor fuel marketed. However, the total cracked gasoline may have an end point from 250 F. to 500 F., vor higher depending entirely on the particular fractionating process and equipment used.

As a rule, the end point on total cracked gasoline is cut with modern methods and equipment to somewhere between 350 F. and 437 F., but variations from this range are permissible within the scope of the invention and may include distillates from other sources such, for instance, as those made by polymerization of hydrocarbon gases and sulphur bearing distillates from other sive to the herein described process may have the following Engler distillation gures:

The distillation characteristics of such unsplit distillate, or an unsplit distillate of closely similar boiling range will, of course, vary and when the same are split to be treated according to the described process there will be some variations in result.

The following table illustrates distillation characteristics of Various percentage splits taken from the processing of different stocks.

Fraction Light Heavy Light Heavy Light Heavy Approximate per- Percent Percent Percent Percent Percent Percent centage o cut.. 30 70 50 50 60 40 Engler, I. B. 1)-... 65 202 82 294 82 323 5 70 228 105 303 114 330 238 116 308 126 333 252 134 317 148 337 266 150 321 170 341 280 168 327 190 345 296 186 335 210 350 314 200 343 226 356 332 214 353 240 363 350 228 364 256 370 370 244 376 270 383 386 386 393 400 276 402 313 407 The above figures are merely used by Way of illustration and it must be understood that the invention is not limited to any particular percentage of cut for treatment, or boiling range, or concentration of acid, but is only limited by the scope of the appended claims.

This application is a division of my co-pending application Serial No. 50,206, led November 16, 1935, and which has issued as Patent No.

2,219,109, October 22, 1940.

I claim:

1. The hereinbefore described process of purifying a cracked petroleum hydrocarbon oil which comprises intimately mixing and reacting with the oil a straight run sulphuric acid sludge to form a mixture of partially puried oil and cracked acid sludge, and separating the oil from the cracked acid sludge.

2. The hereinbefore described process of purifying a cracked petroleum hydrocarbon oil which comprises effecting removal of a large proportion of contained sulphur compounds by intimately mixing the same With a straight run sulphuric acid sludge that is decient in sulphur compounds, and separating the largely desulphurized oil from the cracked acid sludge, whereby the strength and quantity of the acid required for nal purification and the time of reaction may be substantially reduced and the desirable sulphur reduction be obtained with less tendency to polymerization of unsaturated hydrocarbons.

3. The herein described process of purifying a cracked hydrocarbon oil Which comprises subjecting a straight run hydrocarbon oil fraction to treatment with sulphuric acid and separating therefrom the resultant acid sludge, intimately mixing and reacting the cracked hydrocarbon oil with said sludge, and separating the acid sludge product of the last named treatment from the cracked oil.

4. 4The process of purifying a cracked petroleum hydrocarbon oil which `comprises intimately mixing and reacting with the oil a straight run sulphuric acid sludge together with a minor quantity of fresh sulphuric acid to increase the acid concentration of the sludge and separating the purified oil from the resulting acid sludge.

THOMAS F. MCCORMICK. 

